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pablogs9 merged 1 commit into from
Apr 26, 2022
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Update RMW configuration #369

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6 changes: 4 additions & 2 deletions _docs/tutorials/advanced/microxrcedds_rmw_configuration/index.md
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Expand Up @@ -36,14 +36,16 @@ It is achieved by splitting the raw buffer into chunks, each of which contains a
The size of the best-effort and reliable stream can be configured by two sets of CMake flags.

* `UCLIENT_UDP_TRANSPORT_MTU`, `UCLIENT_TCP_TRANSPORT_MTU` and `UCLIENT_SERIAL_TRANSPORT_MTU` (depending on the transport selected): these flags control the size of the best-effort stream buffer which matches with the size of each chunk of the reliable stream.
* `RMW_UXRCE_MAX_HISTORY`: sets the number of slots for the reliable streams.
* `RMW_UXRCE_STREAM_HISTORY`: sets the number of slots for the reliable streams.

The size of the stream sets indirectly the maximum message size (MMS) of the micro-ROS application.
This MMS is (`UCLIENT_<XXX>_TRANSPORT_MTU` - 12 B) for best-effort messages and (`UCLIENT_<XXX>_TRANSPORT_MTU` * (`RMW_UXRCE_MAX_HISTORY` - 12 B)) in the case of reliable messages.
This MMS is (`UCLIENT_<XXX>_TRANSPORT_MTU` - 12 B) for best-effort messages and (`UCLIENT_<XXX>_TRANSPORT_MTU` * (`RMW_UXRCE_STREAM_HISTORY` - 12 B)) in the case of reliable messages.

The use of best-effort or reliable stream is handled by the `rmw_qos_reliability_policy_t` set in the `rmw_qos_profile_t` for a particular publisher or subscription.
In the case of `RMW_QOS_POLICY_RELIABILITY_BEST_EFFORT` best-effort streams are used and for `RMW_QOS_POLICY_RELIABILITY_RELIABLE` reliable streams are used instead.

More details about the micro-ROS middleware can be found in the [Micro XRCE-DDS documentation](https://micro-xrce-dds.docs.eprosima.com/).

### rmw-microxrcedds

rmw-microxrcedds uses static memory for allocating the resources associated with the `rcl` and `rclc` entities.
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